The development of highly automated cameras capable of being folded into a thin, compact shape suited for convenient carrying as described, for instance, in U.S. Pat. Nos. 3,750,551; 3,744,385; 3,731,608; and 3,714,879 has generated a corresponding requirement for a relatively inexpensive disposable battery power supply. To provide the somewhat specialized power requirements for the instrumentalities of the camera while at the same time maintaining requisite compactness, a flat, multicell primary battery is required which exhibits a low internal impedance to produce a relatively high current output for powering motor driven film processing and reflex optics, cocking assemblies along with shutter control features. During this powering activity, the battery is called upon to maintain perdetermined voltage levels required to operate integrated logic control circuits.
For purposes of consumer convenience as well as the maintenance of the requisite compactness of the camera system, as described in U.S. Pat. No. 3,543,662, the flat batteries preferably are pre-packaged within a film-laden cassette assembly and generally take the area dimensional configuration of one film unit therewithin. Accordingly, a disposable power supply is combined with a disposable film cassette thereby permitting requisite compactness and thinness of the resultant camera system while assuring a continuously replenished or fresh and active power supply.
To remain practical within the above-described camera system, the multicell flat batteries must be structured to exhibit an assured or reliable shelf life concomitant with their copackaged film unit. Such reliability is mandatory inasmuch as any dysfunctions on the part of the battery component of the cassette assemblage well may result in the wasting of an entire film package. When considered from the viewpoint of high volume manufacture and packaging, however, an inexpensively assembled flat laminar multicell battery format necessarily is somewhat delicate. For instance, the laminar, multicell pile structures are called upon to perform efficiently without resort to compressive packaging techniques and the like utilized in more conventional batteries. One technique for maintaining necessary laminar integrity looks to the utilization of polymeric adhesives and the like to adhere "patches" of electrode active material to electrically conductive polymeric collector sheet surfaces. As an example, U.S. Pat. No. 3,770,504 describes the predeposition of particulate electrode material upon a carbon impregnated polymeric current collector surface to form a "patch-type" electrode structure. Such assemblies subsequent to patch deposition are combined in combination with a gel electrolyte and sheet separator material to derive a multicell battery.
A flat battery structure from which enhanced current drain capacities are available is described in a copending application for U.S. Patent of S. A. Buckler, Ser. No. 495,681, now abandoned, filed Aug. 8, 1974, entitled "Flat Battery" and assigned in common herewith. This battery includes both positive and negative active components in an aqueous slurry form as particulate dispersions with electrolyte and hydrophillic polymeric binder or dispersant. The electrode particles within the slurry are present in a concentration per unit area which is effective to provide an electrically conductive dispersion and, in consequence of higher surface availability of electrode materials within the electrochemical system, batteries of a desirably broad range of current capacity are readily designed and manufactured. In another commonly assigned copending application for U.S. Patent, Ser. No. 495,628, now abandoned, filed Aug. 8, 1974 by E. H. Land, entitled "Flat Battery", a battery structure of an enhanced output capacity is described as incorporating a laminar cell structure having a planar cathode assembly including a current collector carrying on one surface, in order, a first cathode mix comprising a particulate dispersion of cathode mix particles in a binder matrix and a second cathode mix comprising a particulate dispersion of cathode mix particles with a hydrophillic binder disposed within aqueous electrolyte, i.e., in slurry form.
In addition to the necessity for maintaining the laminar integrity of the flat battery structures, the peripheral borders of their sheet-type electrochemically active components must both be sealed with a high degree of integrity and the electrically conductive components thereof must be protected from shorting effects and the like. Improved peripheral sealing techniques have been described, for instance, in a copending application for U.S. Pat. No. by R. Fancuillo et al, Ser. No. 536,379, filed Dec. 26, 1974, entitled "Flat Battery", now abandoned and assigned in common herewith. The peripheral seal discussed therein contemplates a continuous frame-type electrically insulative sheet sealing component selectively dimensioned to avoid edge shorting effects as well as to derive a rigid peripheral structure in the final battery composite.
Primary battery structures tend to generate gases or volatile effluvia in the course of electrochemical activity. Where such conditions are encountered within the laminar structures described above, delamination effects may occur resulting in increased internal impedance or total failure.
Accordingly, an effective accommodation for such phenomena will improve battery shelf life and performance. The techniques utilized, however, should provide for the removal of effluvia while blocking outer atmospheric influence and while maintaining required moisture levels of the electrolyte or slurries within the structure. Some venting techniques for flat batteries are described, for instance, in U.S. Patent No. 3,877,045 and copending application for U.S. Pat. by E. H. Land, entitled "Novel Battery", filed Oct. 3, 1973, Ser. No. 403,039, and now abandoned both assigned in common herewith.
The selection of component materials, their shapes, interrelational geometries and the techniques of their practical assembly has continued to require improvement. A succession of design alterations to structure, material or assembly may remain somewhat subtle, but also may combine to achieve needed performance.